Stepwise formation of crystalline apatite in the biomimetic coating of surgical grade SS 316L substrate: A TEM analysis

The present communication reports an interesting observation on stepwise development of crystallinity along with change in elemental composition of the HAp crystals, precipitated on SS 316L substrates (4 mm × 5 mm × 1 mm) by biomimetic route. The SS 316L substrates were incubated up to 6 days in simulated body fluid (SBF) at 37 °C with a periodic replacement of freshly prepared SBF at 48 h intervals. X ray diffraction (XRD) analysis of coated substrates revealed phase pure hydroxyapatite (HAp) as the only phase present in the coating. Transmission electron microscopy (TEM) images of the coating showed a gradual transformation of core shell type spherical HAp crystal into elongated forms over a period of 6 days of incubation of SS 316L substrate in SBF. The elemental composition of the deposited HAp phase was also changed with increase in exposure time of SS 316L to SBF as indicated by the energy dispersive spectra (EDS) of coated substrates.